The invention relates to the treatment of porous masonry and wood surfaces to control algal defacement by the application of a microbicidal composition.
Microbial colonization of masonry construction materials significantly contributes to defacement and weathering. This can be caused by a diverse community of microorganisms that includes bacteria, fungi and algae. Growth of these organisms and thus the severity of defacement and biodeterioration is dependent on many factors, including porosity of the masonry material, pore size and distribution, permeability, effective pH, surface charge, nutrient availability, presence of light, temperature and relative humidity and wetting by rain.
Physiochemical characteristics such as the porosity, pore size distribution, permeability, surface charge and alkalinity vary from material to material and even within samples of the same material. These characteristics can affect the performance of biocidal treatments. Consequently, performance and effective application-rate ranges must be based on the response of treated porous masonry and wood substrate materials to microbial challenge.
Typical approaches to the control of microbial growth on or from within masonry materials are (1) limitation of the moisture content of the construction material using water repellants, and (2) treatment with microbicidal chemicals. Chemical treatments that have been used with some success are: hypochlorite, organotin, organomercurial, quaternary ammonium salt, chlorinated phenolic, borate and phosphoric acid. The use of many of these chemical biocides has been restricted or entirely banned due to concerns for significant environmental impact. Some of the chemical treatments may not be supported under the European Union Biocidal Products Directive due to high costs.
Extreme cases of defacement have been observed of newly-constructed masonry surfaces (non-painted) and freshly painted masonry by algae commonly encountered in the warm humid climates of the Pacific Rim and Mediterranean regions of the world. Similar defacement has also been reported in temperate regions. If left untreated for an extended period of time, the masonry substrate can incur permanent damage, leading to attendant costs for repair and replacement.
It is known from U.S. Pat. No. 5,917,094 that a 2-propenal-releasing emulsion homopolymer can be produced by adding 2-propenal that is at least 95% by weight pure, to a composition of an alkali hydroxide under specified conditions, and then adjusting the pH to the range of from 5 to 7. The only use disclosed for such 2-propenal homopolymers are in aqueous systems, such as paints and other architectural coatings. The 2-propenal is released when a pH is greater than 7, thereby producing a biocidal affect in these systems. A controlled release of 2-propenal to maintain apparently minimum effective limit value of 0.7 ppm in the aqueous systems tested reportedly exceeded 400 days.
It is known from the prior art to use a 2-propenal copolymer as an in-can preservative to prevent spoilage of aqueous liquid products, such as decorative coatings, adhesives, metal working fluids and inks. When used in these industrial applications the 2-propenal copolymer is supplied in the form of an aqueous composition at about 50 weight percent as the copolymer and is mixed with the aqueous liquid composition, typically in a percentage by weight in the range of from about 0.25% to 1%.
It is also known from the prior art to add 2-propenal molecular or oligomer form to outdoor containments lined with polymer membranes, waste water storage, and treatment ponds and drainage ditches to control the growth of water-borne algae. Such applications do not appear to have included use of a 2-propenal copolymer.
The art has not been found to disclose the use of a copolymer of 2-propenal for application to solid porous surfaces to prevent the defacement of the surface by organisms that colonize such surfaces, e.g., terrestrial algae.
It is therefore a principal object of the invention to provide a safe and efficacious method for applying an environmentally benign composition having anti-microbial activity as an algacidal treatment for masonry and wood surfaces subject to algal growth and defacement.
It is also an object of this invention to provide a quantitative application rate for 2-propenal copolymers that will provide extended time-release anti-microbial protection for the surface of porous construction materials exposed to algal growth and defacement.
The above objects and other benefits and advantages are attained by the practice of the method of the invention in which a time-release aqueous biocidal composition of a 2-propenal copolymer is applied to the porous surface of a construction material selected from the group consisting of stone, concrete, brick and wood and the biocidal composition is maintained in contact with the porous surface for a sufficient period of time to saturate a portion of the construction material below the surface with the biocidal composition. The surface of the construction material is then allowed to dry.
If desired, after drying the surface of construction material can be coated with a decorative architectural coating, or paint.
As used herein, the term xe2x80x9c2-propenal copolymerxe2x80x9d means a composition of 2-propenal prepared in accordance with the disclosure of U.S. Pat. No. 6,060,571, the disclosure of which is incorporated herein by reference. A particularly preferred composition is the reaction product of 2-propenal and propylene 1,2-glycol prepared in accordance with Example 4 of U.S. Pat. No. 6,060,571 as described below.
In a preferred embodiment, the biocidal compound constitutes at least about 0.25% by weight of the aqueous composition applied to the construction material. In an especially preferred embodiment the 2-propenal copolymer is about one percent by weight of the applied composition.
The aqueous biocidal composition can be applied by conventional methods including spraying, brushing and dispensing a liquid stream from a horizontal feed line and allowing the composition to stream down the face of an existing structure.
In a particularly preferred embodiment, new construction materials are treated by immersing the construction material in a bath of the biocidal composition, or by dipping or soaking one of more of the surfaces of the material that will be exposed to biological growth in a treatment zone containing the biocidal composition. This method of application is particularly effective and efficient, since the duration of the soaking time in the specific concentration of the biocidal composition can be used to provide the desired degree of time-release protection. The depth of penetration and saturation can be determined from a relatively small sample of the particular construction material, whether it be a natural stone such as sandstone, a fired brick, a section of pre-cast concrete or so-called cast stone or any of the various species of wood that are used for construction. The immersion, dipping and soaking methods of application also have the particular advantage of assuring a uniform concentration of material over the entire surface treated, thereby avoiding potential problems is associated with the application of the aqueous biocidal composition by brushing or spraying to existing structures.
In a further preferred method of practicing the invention for providing a time-release protection to new construction materials, the individual elements, i.e., bricks, natural stone, concrete blocks or pre-cast articles, wood, or the like, are conditioned to a uniform moisture content prior to application of the biocidal copolymer composition. For example, when construction materials are stored in a climate having high humidity, it is preferred to dry at least the surface to be treated with the biocidal copolymer composition to dry out excessive moisture so that the region at the exposed surface can absorb the optimum volume of the applied composition.
It is well known in the wood products industry to kiln dry lumber to minimize twisting and other deformation that can occur to render the material unsuitable. Such dried or otherwise cured wood construction materials will be likely to absorb a predictable amount of the treating composition. Wooden construction materials -so treated can be further treated with other conventional preservatives in accordance with methods known to the art.
Several application methods are suitable for the practice of the invention in the treatment of seasoned wood products with aqueous preservative compositions, including thermal treatment and pressure treatment.
Thermal treatment also known as hot and cold bath treatment, involves immersion of the wood products in a hot preservative composition and then a cool preservative composition. The hot composition causes air in the wood to expand; the subsequent immersion in a cool preservative composition causes the air in the wood to contract creating a vacuum that draws preservative into the wood.
The invention can also be employed in prior art pressure treatments such as the full-cell and empty-cell processes. In the full-cell process, dry wood products are loaded into a retort and a vacuum is drawn to remove air from the wood. The preservative composition is then introduced into the retort. When the retort is filled with composition, pressure is applied to force the composition into the wood. When absorption is complete the pressure is released and the treated wood products are removed.
In the empty-cell process, preservative composition is introduced into the retort at atmospheric pressure and then the retort is pressurized. When absorption is complete, the pressure is released and the remaining preservative composition is withdrawn to storage. The pressure inside the retort is reduced to remove any excess preservative composition from the wood products. An advantage of this process over the full-cell process is that similar penetrations of the wood can be obtained with a reduced use of preservative composition. As will be understood by one of ordinary skill in the art from the above descriptions, the method and preservation system of the invention can be employed in other known treatment processes.
Exterior wooden surfaces that are coated with pigmented decorative paints also benefit from treatment of the wood substrate in accordance with the invention. These painted surfaces, as well as bare wooden surfaces, are subject to defacement by microorganisms such as highly colored filamentous algae. Treated wood serves as a source of the biocidal 2-propenal copolymer for longterm protection of painted surfaces from biological defacement. The 2-propenal copolymer composition can also be formulated with other biocidal compounds in order to broaden the spectrum of antimicrobial activity. Wetting agents, such as nonionic surfactants and cosolvents such as propyleneglycol can be used as adjuvants to promote adsorption of the preservative composition into woods that are otherwise difficult to penetrate.
Following treatment with the aqueous biocidal copolymer composition and drying of the surface, the construction material can be painted with a decorative architectural coating. Coating materials that have been found suitable for use in connection with the practice of the invention are acrylic, vinylacrylic and alkyd modified latex paints. These types of coatings are sufficiently porous to allow the active material to pass through and exhibit its biocidal activity. The painted surface also slows the leaching of the active compound at the surface when exposed to direct rainfall, water spray and the like.
As used herein, the terms xe2x80x9ctime-releasexe2x80x9d or xe2x80x9ccontrolled releasexe2x80x9d means the essentially continuous release of an amount of biocidally active material that is effective to inhibit or control the growth of defacing and/or damaging algae for an extended period of time that exceeds about six months.
The advantages of treatment with a controlled or time-release copolymer include the following:
1. Treatment with the copolymer offers long-term protection versus that provided by short-term treatments, such as hypochlorite.
2. The copolymer is not a charged moiety and the binding to mineral surfaces that occurs with some cationic biocides does not occur.
3. The copolymer is not an inorganic nutrient, as is the residual phosphate from commonly-used masonry treatments containing phosphoric acid.
4. The copolymer is non-chlorinated and non-metallic and avoids the environmental concerns raised by the use of compositions containing chlorine and metals.
The following examples and detailed description are provided to illustrate to one of ordinary skill in the art the method and products of the invention.
The first tier screening test described herein demonstrates the efficacy of the biocidal copolymer as an algaecidal treatment for masonry materials commonly used in Europe, the Pacific-Rim and the United States. Brick, sandstone and concrete were treated and challenged with an algal inoculum. The test results also establish appropriate application guidelines for the concentration and application rates of the 2-propenal copolymer compositions that are applied in situ to various uncoated construction materials.
Materials and Methods
In order to demonstrate the efficacy of the method of the invention, samples of materials representative of masonry products from different regions of the world were subjected to the test protocol. Masonry samples were treated and either (1) uncoated; or (2) coated with paint and then exposed to severe challenge with an inoculum of algae known to exhibit high growth activity in warm, humid climates. The tests were performed in microenvironments constructed of large petri dishes containing a nutrient medium. Surface defacement and zones of inhibition were rated according to established practice and photographed. A variety of pretreatment regimes were used to establish guidelines for application of a composition of 2-propenal copolymer.
Test Chamber
Test chambers simulating microenvironments were provided for the purpose of demonstrating the efficacy of the invention. Plastic petri dishes measuring 90 mmxc3x97250 mm. were partially filled with approximately 50 ml of Allen""s nutrient agar medium. Masonry test specimens in the form of small blocks were placed on the hardened agar medium in the petri dishes and then inoculated with an algal cell suspension. The petri dishes were then placed in an incubator and the surface of the masonry blocks observed and rated for algal growth at weekly intervals for six weeks.
Inoculum
Five to fourteen day cultures of the green alga, Chlorella sp (ATCC 7516), were harvested to sterile distilled water and suspended. Each masonry block was inoculated with 1 ml of Chlorella sp suspension.
Preparation of Biocidal Compositions
Biocidal compositions ranging in concentration from 0.25 to 5.0 weight-percent of 2-propenal copolymer were prepared from an aqueous stock preparation of commercially available 50 weight-percent 2-propenal copolymer by dilution with water. The commercial product utilized in the work reported is sold under the trademark NUOSEPT(copyright) APC-P by Degussa Corporation of Parsippany, N.J.
Alternatively a composition that is the reaction product of 2-propenal and propylene 1,2-glycol is prepared in accordance with Example 4 of U.S. Pat. No. 6,060,571 as follows: